1. Field of the Invention
The present invention is related to the field of vision correction and, more particularly, to eyeglasses using hetero-chromic filters for improved visual contrast.
2. Description of the Related Art
Most individuals start to lose quality of vision by the end of the fourth decade of life and especially past the age of 50. With the xe2x80x98greyingxe2x80x99 of America, even when the eye is emmetropic or the corrected vision approximates 20/20 by means of a spectacle prescription and/or contact lenses, there are regressive decrements in visual quality that can be attributed to changes in the ocular media and retina. These changes are characterized by a decrease in retinal illuminance, increased xe2x80x98disability glare,xe2x80x99 reduced foveal flicker sensitivity, and loss of contrast sensitivity.
Adult levels of contrast sensitivity are reached at approximately age 7, and there follows a protracted leveling period until onset of midlife decline. In and of itself, contrast sensitivity bears a direct relationship to visual acuity capability (superacuity=20/20 or better; normal acuity=20/20 or less.) Well understood is that under the best of refractive circumstances, we lose at least one letter of visual acuity every 20 years. Contrast sensitivity for letters, past age 65, then undergoes significant loss with further aging. Even prior to the detection of early senile cataract formation, there is observably lessened intensity of the 4th Purkinje Image, as measured by the Lens Absorption Meter (LAM). Further, with aging, most individuals will encounter gradual loss of correctable vision because of cataract formation. Macular degeneration is also becoming a greater threat to vision in the elderly. Whatever the cause, visual losses usually do not proceed symmetrically but, at any point in time, are measurably greater in one eye that the other.
In addition to advancing age, as the daylight hours shorten during the late fall and toward the mid-winter months, longer hours of darkness impact adversely upon our visual perception. At dusk there is poor visual contrast for driving, and our ability to accurately judge distances lessens. Also, on rainy nights, reflections from vehicles and street lights are especially distracting.
Efforts at enhanced vision perception have previously been undertaken in connection with color blindness and improved color perception, as representatively disclosed in U.S. Pat. Nos. 5,917,573, 4,300,819 and 3,586,423 to Davis, Taylor and Zeltzer, respectively. Such devices rely upon one or more lenses from the long end of the visible spectrum, namely red, to aid in the distinguishing and perception of colors.
Analyglyphic devices have also been developed which receive long (red) and short (blue/green) wavelengths separately in each eye for stereoscopic viewing. However, due to the highly dissimilar wavelength images, significant color-retinal rivalry is induced, with associated subjective xe2x80x9cwashingxe2x80x9d of red and green colors as perceived by the user of the device. When significant color-retinal rivalry persists, the brain will begin to suppress either one of the two images, resulting in loss of binocular vision.
Therefore, a need exists for a light filtration device that can enhance visual contrast and overall vision quality, independently of improvements in visual acuity, and without disrupting binocularity.
In view of the foregoing, one object of the present invention is to overcome the difficulties associated with poor contrast sensitivity, particularly in low or scattered light environments, such as is encountered during dusk or night-time driving, or on cloudy, rainy or snowy days.
Another object of the present invention is to provide eyewear having hetero-chromic filters to enhance visual contrast.
A further object of the present invention is to provide within a pair of eyeglasses viewing lenses of two different colors which, while inducing color-retinal rivalry between the two eyes, are sufficiently close in wavelength to avoid loss of binocular vision.
Yet another object of the present invention is to provide eyewear, particularly eyeglasses or contact lenses, in which one lens provides a pale green filter and the other lens provides a slightly darker yellow filter in order to enhance visual contrast.
A still further object of the invention is to enhance prescription eyewear with the addition of respective green and yellow filters within the corrective lenses.
In accordance with this and other objects, the present invention is directed to eyewear in which visual contrast is enhanced using hetero-chromic filters. When employed with glasses, one lens that has been tinted pale green and a second lens that has been tinted to be a slightly darker yellow, are placed within an eyeglass frame. The resulting pair of glasses, when worn, creates limited color-retinal rivalry between the two eyes and encourages better visual contrast resulting in better quality of vision, especially at night.
These and other objects of the invention, as well as many of the intended advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings.